Large-caliber pipes of the construction described are used mainly for underground laying, namely for sewage and waste water purposes. When laid underground they are subject to quasi-hydrostatic stresses from the earth pressure and such stresses have to be taken up by an adequate annular rigidity. In subsidence areas there may additionally be considerable bending stresses which have to be taken up by elastic deformation and which require a high stability of the complete pipe, there otherwise being the risk of rupture due to stability failure.
The pipes described in German Patent 23 08 417 are constructed from a hollow plastic profile of square or rectangular external cross-section and round internal cross-section. The arrangement is such that the hollow plastic profile side walls welded to form a butt-welded seam are about 50% thinner than the free hollow profile walls, and the free hollow profile walls are so designed that the deformation stresses arising from the stressing acting on the underground pipe do not exceed the strength of the butt-welded seams. These known pipes have proved to be satisfactory. They can undergo sufficient elastic deformation and takeup the stresses without any risk of rupture due to stability failure. However, to ensure this, the hollow profile walls must be made appropriately thick. This results in a relatively considerable weight of the known pipes for a given caliber and given stress parameters.